In agriculture, the use of hydraulic motors is well known for use in driving various aspects of agricultural equipment, notably fans used on air seeders. The width of such air seeders has increased substantially such that implements 60 feet wide are now common. As well the amount of seed, fertilizer, and like agricultural materials that are being applied on each acre of land has increased. Significant amounts of seed and fertilizer, for example, are commonly applied at the same time by the same fan. These developments have contributed to a need for higher capacity fans, which in turn require more hydraulic power from the tractor pulling the air seeder, which tractor also typically provides the hydraulic power supply to operate the fan. Hydraulic motor driven fans on newer drills typically consume 12 to 15 gallons of fluid per minute (gal/min).
Hydraulic motors on agricultural equipment are typically connected to the tractor's hydraulic supply. A pair of hydraulic lines run from the fan, and are connected by a pair of quick couplers at the back of the tractor to a valve block. Pressurized hydraulic fluid is supplied to the valve block by a pump powered by the tractor engine. Hydraulic fluid flows out of one tractor quick coupler, through one hydraulic line to the hydraulic motor driving the fan, then back through the other hydraulic line and through the other tractor quick coupler back into the tractor hydraulic supply system. Typically a lever or the like is activated by the tractor operator to control the flow of hydraulic fluid from the tractor's hydraulic supply through the quick couplers and hydraulic lines to the hydraulic motor driving the fan. Thus the hydraulic motor, hydraulic lines, quick couplers and valve block form a hydraulic circuit through which hydraulic fluid flows under pressure to drive the fan. The operator moves the lever to cause hydraulic fluid to flow or stop flowing to turn the fan on and off.
Many original air seeders used a separate internal combustion engine to drive the fan, but the simplicity and economy of hydraulic motor drives has led to their prevalence. Obtaining sufficient fluid flow from tractors has been a problem to a greater or lesser extent since air seeders were introduced. The hydraulic pumps and valve systems on agricultural tractors provide a range of greater and lesser capacities. The pumps and valve blocks on older tractors were not designed to provide the high volumes of fluid required by air seeder fans. The size of the ports restricts fluid flow at higher rates.
Shortly after hydraulics were introduced to agricultural equipment, quick couplers were introduced for quickly and conveniently connecting hydraulic devices, primarily at that time hydraulic cylinders, to tractor hydraulic power supplies. The design of quick couplers has not changed significantly over the years partially due to the industries desire for standardization of the quick coupler. These standard quick couplers were not designed for the high flow rates required for hydraulic motors, and restrict fluid flow at higher rates.
Forcing the high flows of fluid through the restrictive ports and quick couplers causes back pressure for the fluid leaving the tractor and a second back pressure for the fluid returning to the tractor. These back pressures have several negative effects. Extra heat built up from the back pressures tax the tractor hydraulic fluid cooling system. Power is wasted as a result of the back pressures. The back pressures ultimately limit the tractors capacity to produce adequate fluid volume and pressure required by hydraulic motors, as well as other conventional implement functions such as raising and lowering, moving markers in and out, and so forth.
The back pressures result in a pressure drop between the hydraulic pump and the hydraulic line that increases significantly as fluid flow increases. The pressure drop for 15 gal/min leaving the tractor through the valve block and quick coupler is in the order of 250 to 400 pounds per square inch (psi). In addition, there is a similar pressure drop of 250 to 400 psi for fluid returning to the tractor through the quick coupler and valve block. Thus the total pressure drop of fluid leaving and returning to the tractor (not counting pressure drop at the fan) is between 500 and 800 psi on a hydraulic system with a 2100 psi operation pressure. This 500–800 psi represents a loss of 25% to 40% of the capacity.
In contrast, the pressure drop for 8 gal/min leaving the tractor is in the order of 80 to 100 psi and the same 8 gal/min returning to the tractor creates a similar back pressure of 80 to 100 psi for a total of 160–200 psi.
In order to reduce the back pressure, it is common to provide larger diameter hydraulic lines running back to the hydraulic motor driving the fan, however this does nothing to reduce the pressure drop through the quick couplers and hydraulic valve block of the single circuit, where the same 15 gal/min is required to pass.
Agricultural tractors typically have a plurality of quick coupler connections for connecting the tractor hydraulic power supply to provide controlled hydraulic fluid under pressure to the various hydraulic devices used on agricultural implements. Each set or pair of quick couplers is commonly called a “remote”, as in remote connection, and hydraulic fluid flow in the hydraulic supply circuit provided by each remote is typically controlled by a lever at the operator's position. Recently it is sometimes known to provide electrical control of remotes as well, where the lever is replaced by a switch. The operation, however, is basically the same, as the operator can direct flow out a first line and back through a second, or out the second and back through the first, or shut off fluid flow altogether. Flow controls are sometimes provided as well for varying the amount of fluid flowing through a remote, in order to vary response time for a hydraulic cylinder, or the speed of a hydraulic motor.
In this way, each hydraulic function on an air seeder can be controlled substantially independently. A tractor with four remotes will typically have one connected to the fan, one to raise and lower the furrow openers, and one for raising the implement wings into a transport position. Further functions may be connected to the fourth remote, such as folding markers, another hydraulic motor driving an auger to fill the hoppers with seed and fertilizer, or the like. Air seeders are also known that use “active hydraulics” to provide biasing forces to push implement wings down to improve penetration, or to bias individual furrow openers down, much as a conventional spring would do.
These further functions typically will require much less hydraulic fluid flow than the hydraulic motor driving the fan. An active hydraulic circuit for example might only require a flow of two to five gal/min. Raising and lowering functions draw fluid only when activated.